Tomorrow BP will attempt to “top kill” the well that is spewing-who knows how much-oil into the Gulf of Mexico(GOM). BP estimates somewhere around 5000 bbs/day are escaping from the collapsed riser and blowout preventer(BOP), but researchers at Purdue, using estimates from live feeds, estimate the flow somewhere between 40000-100000 bbs/day.
The Purdue results appear to be high; top producing wells in the GOM generate about 50000 bbs/day. This well’s location is in an area(Miss. Canyon Block 252) of the gulf that isn’t as productive as some other areas. So, I tend to accept BP’s estimates… within a margin of error, of course.
The “top kill” procedure involves pumping drilling mud into the BOP in pressures greater than the escaping oil and gas. The ideal is that the pressure from the pumps combined with the weight of the overlying column of mud will displace the hydrocarbons in the production string of casing from the well head to the base of the well, and then fill the casements-effectively blocking the leak. Cement will then be pumped into the string to seal the well… if all goes according to plan.
And, therein is the problem-nothing has gone according to plan. BP, and others, have speculated that the reason for the initial blow out was that a poor seal in the contact between the production casing and the protective casing at the base of the well. Apparently, the blow by was noted by engineers when mud pit volume increased out of proportion-well logs indicate that twice they stopped pumping mud in the two hours before the blow out!
In yesterday’s press briefing, BP noted that in finding cause of the blow out, the “investigation is focused on the following seven mechanisms.”
1. The cement that seals the reservoir from the well;
2. The casing system, which seals the well bore;
3. The pressure tests to confirm the well is sealed;
4. The execution of procedures to detect and control hydrocarbons in the well, including the use of the BOP;
5. The BOP Emergency Disconnect System, which can be activated by pushing a button at multiple locations on the rig;
6. The automatic closure of the BOP after its connection is lost with the rig; and
7. Features in the BOP to allow Remotely Operated Vehicles (ROV) to close the BOP and thereby seal the well at the seabed after a blow out.
Regarding 3 above: rumor has it that a well known, and very expensive geotech firm was on the platform to do cement-bond logs, and that in a hurry to get off site(so the completion crew could move in???), BP’s top guy on-site put a stop order on the c-b logs. One thing is known-the geotech firm confirmed that they pulled their people 6 hours before the blow out- which was 14 hours after the final cement job for the seal started pumping.
There are other rumors floating around that the well was “kicking”… hard, and that for that reason, a “dump kill” was recommended hours before the blow out.
I guess that we will find out in Congessional hearings.
There are a lot problems with the “top kill” plan. Some have speculated that the mud, under those pressures, will fracture the formation, and that this will lead to greater flow at the base. Fracking wells is a common procedure to increase production in reservoirs, but as the sediments in the gulf are very permeable(around 30%), and barely consolidated, it doesn’t seem that if the formation does frak, that it would a problem.
Though, a real possibility is that blockages in the string will force the mud out the BOP, eroding what constraints are inhibiting the flow. Another danger could be a blow out in the containment string near the surface… if the seals are bad, and there are blockages, the mud could force its way into the containment nearer the surface where that part of the string doesn’t generally encounter those types of pressures.
BP estimates for success are 60-70%. If unsuccessful, a “junk” shot will be attempted in which various sized rubber balls will be injected into the system; If that fails, an attempt will be made to cut off the top of the damaged BOP and affix the Lower Marine Riser Package(Top Hat) to the clean surface.
I wish the crews luck tomorrow. Hopefully, by tomorrow night the well will be sealed… but I doubt it. From the opinions of engineers and geologists, that I have read, this thing might be flowing until the relief wells are finished in the late summer.
Note: I am not a petroleum geologist, and I do not work in the industry. If I have misconstrued anything, or is there is more to add, let me know in the comments.